body{
    margin: 0;
    padding: 0;
}

ul{
    list-style: none;
}

.container{
    padding-top: 3%;
    padding-left: 3%;
}

.grid{
    width: 100%;
    padding-left: 0;
    margin: 0;
}

.grid::after{
    content: "";
    display: block;
    clear: both;
    height: 0;
}

.grid-item{
    display: block;
    float: left;
    margin-right: 3%;
    margin-bottom: 3%;
    background-color: red;
    width: 30.33333%;
    padding-bottom: 30.33333%;/* 格子是正方形的关键，height是设置了会无效 */
    border-radius: 5%;
}